Reversible Pressure-Induced Partial Phase Transition in Few-Layer Black Phosphorus.

The experimental identification of structural transitions in layered black phosphorus (BP) under mechanical stress is essential to extend its application in microelectromechanical (MEMS) devices under harsh conditions. High-pressure Raman spectroscopic analysis of BP flakes suggests a transition pressure at ∼4.2 GPa, where the BP's crystal structure progressively transforms from an orthorhombic to a rhombohedral symmetry (blue phosphorus, bP). The phase transition has been identified by observing a transition from blueshift to redshift of the in-plane characteristic Raman modes (B2g and Ag2) with increasing pressure. Recovery of the vibrational frequencies for all three characteristic Raman modes confirms the reversibility of the structural phase transition. First-principles calculations provide insight into the behavior of the Raman modes of BP under high pressure and reveal the mechanism responsible for the partial phase transition from BP to bP, corresponding to a metastable equilibrium state where both phases coexist.

High-throughput identification of spin-photon interfaces in silicon.

Color centers in host semiconductors are prime candidates as spin-photon interfaces for quantum applications. Finding an optimal spin-photon interface in silicon would move quantum information technologies toward a mature semiconducting host. However, the space of possible charged defects is vast, making the identification of candidates from experiments alone extremely challenging. Here, we use high-throughput first-principles computational screening to identify spin-photon interfaces among more than 1000 charged defects in silicon. The use of a single-shot hybrid functional approach is critical in enabling the screening of many quantum defects with a reasonable accuracy. We identify three promising spin-photon interfaces as potential bright emitters in the telecom band: [Formula: see text], [Formula: see text], and [Formula: see text]. These candidates are excited through defect-bound excitons, stressing the importance of such defects in silicon for telecom band operations. Our work paves the way to further large-scale computational screening for quantum defects in semiconductors.

Effect of substitutional impurities on vibrational properties of zircon: a first-principles study.

Density-functional theory was used to investigate the effect of atomic impurities on the structural and vibrational properties of zircon (tetragonal ZrSiO4). Atomic impurities considered include radioactive elements U and Th, as well as Hf, Sn, and Ti, substituted on the Zr-site. Using the supercell approach to model a range of substitutional concentrations, impurities were found to cause changes in the volume of the host lattice. This effect was shown to be partially equivalent to the application of a lattice strain. This quantum-based finding is in excellent agreement with the heuristic lattice-strain model traditionally employed in the geosciences to account for the compatibility of impurities in host lattices. Vibrational properties of substituted zircon were also investigated in order to provide a quantum mechanical understanding of Raman spectroscopy measurements on natural zircon. The computational analysis reproduces existing experimental data reported for uranium-substituted zircon and provides general predictive trends for other impurities including Th, Hf, Sn, and Ti. The insights gained by this study regarding the Raman signature of the presence of substitutional impurities set the groundwork for future study of the more substantial lattice disruptions that characterize radiation damage due to alpha decay in zircon.